Many animal and plant viruses use the strategy of proteolytic processing to synthesize functional viral proteins. Investigation of biochemical compounds that inhibit this reaction could lead to the development of methods for the control of viral infection. The objectives of this research are to purify and to characterize a natural protease inhibitor from cowpea embryos. The experimental plans of this project are summarized below: (1) To purify a cowpea embryo protease inhibitor which can strongly inhibit the cleavage of a 200,000-dalton (2OOK) polyprotein coded by the B-RNA of cowpea mosaic virus (CPMV). (2) To biochemically characterize the inhibitor, including determination of basic chemical and physical properties, analysis of the reactivities of the inhibitor towards different proteases, and comparison of the activity of the inhibitor to the activities of chemically synthesized oligopeptides. (3) To determine whether the occurrence of the inhibitor is related to the resistance of different cowpea lines to CPMV infection. (4) To determine the amino acid sequence of the inhibitor through sequencing of cDNA or genomic DNA clones. The long range goal of this project will be to apply the fundamental information obtained in these experiments to develop procedures employing this protease inhibitor in the prevention or treatment of animal and plant viral diseases caused by viruses which use proteolytic processing for replication.